In the past, drainage lines for water and the like have become recognized as being virtually essential alongside roadways, beneath the roadways, for carrying off water from a level beneath the road that may otherwise tend to rise to the level of the road and flood the same.
Generally, such water conduits have been placed at the sides of roads, a few feet below the road, imbedded in gravel or in like loose stone fill that will permit seepage of water to the conduit.
Previously, the conduit comprised a plurality of sections of round spiral corrugated pipe, placed end-to-end. These pipe connections would generally be 6 inches to 8 inches in diameter, in order to carry off the desired flow of water. However, the corrugations on the inside surface of the pipe, over which water would flow, would induce turbulence that would interfere with the streamline flow of water through the pipe. Furthermore, water inlets to such pipe would clog with dirt if they were in the upper half circle of the pipe and if the pipe were positioned such that the water inlets were in the lower half circle of the pipe, the zone of the pipe through which water could be carried was severly limited.
Accordingly, there has been a tendency away from the use of such pipe as drainage conduit, and toward the use of conduit that may be fabricated to have smooth interior surfaces, for more greatly facilitating the free passage of water therealong. Because of the usual smooth surface present in making metal drainage conduit, and the ability of steel to pass water freely therealong, a drainage conduit having a smooth inner bottom surface may be greatly reduced in size, relative to a corrugated drainage conduit, for handling virtually the same flow of water. For example, whereas, with the use of round corrugated drainage conduit, a 6 inch to 8 inch diameter line may be required, a semi-circular conduit with a smooth inner bottom surface may be, for example, 45/8 inches across, and yet may handle the same flow of water.
The use of steel or other metal conduit has been highly desirable, but, in the manufacture of the same, in accordance with manufacturing techniques that require many hand working operations, the use of metal drainage conduit has not reached its potential due to high labor costs for hand operations, limitations upon production speeds, and the like.